If you look at both url's you will see that the only difference is the API-key.
The first url has NO API key, therefore no response.
The second url has API-key and then you get response.
If you open the first url in a browser you will see the message

I seem to be experiencing the same problem, but it does not appear to be related to a specific station.
Out of the last 100 hourly10day API calls (made roughly 2 to 3 hours ago) 22 returned an empty result.
By empty I mean what is shown in the screenshot below.